In the drilling and servicing of wells (e.g., oil and gas wells) the pipe and other equipment which must be placed into the well bore are necessarily subjected to many corrosive fluids of various types which can be quite harmful to the pipe and equipment. Although it has been previously known to place a corrosion test ring inside the pipe string to measure corrosion effects in the interior of the pipe, there has not previously been described any system for measuring corrosion effects on the exterior of the pipe, nor has there been suggested any desirability for attempting to measure such corrosion.